The invention relates to methods and apparatuses for delivering reagents and forming reactive barriers for pollution control.
One persistent global challenge is the management and remediation of pollution. Pollution can take several forms, one of which includes land or soil pollution. Soil at a variety of depths beneath the ground""s surface can become contaminated with pollutants from a wide variety of sources. Soil pollution includes contamination of soil in the Vadose zone, meaning soil that is not saturated with water between the ground surface and a point below the ground surface where the soil becomes saturated with water. Soil pollution can also occur in groundwater, meaning any regions of the soil below the Vadose zone that are saturated with water.
Contamination from a point source in the Vadose zone can disburse outward from the source. Contaminants can also disburse from the Vadose zone into underlying groundwater. Groundwater typically has a gradient or flow pattern, wherein groundwater flows through the saturated soil matrix while solid soil particles remain in place. Accordingly, when contaminants reach groundwater, the contaminants can potentially spread with the groundwater more rapidly than they would otherwise from dispersion in the Vadose zone.
The problem of contaminants spreading by dispersion in the Vadose zone, groundwater flow, or other mechanisms is widely recognized. Accordingly, a wide variety of methods and apparatuses have been developed to counteract contamination of increasingly large areas of soil caused by contaminants spreading.
One such technology provides the creation of reactive barriers in soil that can be contacted with contaminated groundwater or dispersion from contaminated Vadose zone soil. A reactive barrier can be established by digging a trench into which a reactive substance can be placed and then backfilling the trench. One such reactive substance includes zero-valent iron in the form of iron filings that acts as a reducing agent on a variety of contaminants. Groundwater containing targeted contaminants can flow through the iron filings deposited in a trench and flow out of such iron filings as treated ground water.
While some success has been achieved in establishing reactive barriers in trenches, the life of such a barrier is finite. Depending on a variety of conditions, including the level of contamination, the reagents in the barrier will ultimately be consumed. Once the reaction with contaminants ceases, additional reactive materials must again be placed in a trench and backfilled to continue the treatment of groundwater in situ.
It would be very unusual for a reactive barrier, as described above, to maintain its reactivity long enough to effectuate complete treatment of groundwater contaminates. Rather, the most common circumstance is that protection against spreading of contaminates will endure for a time and then cease. Thus, a need exists for reactive barriers that will persist long enough to prevent contaminant spreading as long as the contamination exists. Improved techniques are also needed for efficiently constructing reactive barriers and for creating more effective barriers that minimize the disruption to the existing soil. Such reactive barriers are needed to alleviate the spreading of groundwater contamination as well as Vadose zone contamination. Without such advances, the current challenges of isolating and remediating soil contamination will continue to exist.
In accordance with one aspect of the invention, soil contamination is treated by forming a barrier of oxidized soil material. The oxidized barrier is formed by delivering an oxidizing agent into the ground to oxidize an existing soil component, and the barrier is formed in the path of contaminate migration to neutralize percolating soil contamination. The oxidized material reacts with soil contaminate migrating into the barrier to reduce the level of the soil contaminate migrating through the barrier to acceptable levels. The existing soil component can be a naturally occurring mineral, such as manganese, and the oxidizing agent can be ozone.
In accordance with another aspect of the invention, a reagent delivery method includes positioning reagent delivery tubes in contact with soil. The tubes can include a wall that is permeable to a soil-modifying reagent. The method further includes supplying the reagent in the tubes, diffusing the reagent through the permeable wall and into the soil, and chemically modifying a selected component of the soil using the reagent. The tubes can be in subsurface contact with soil, including groundwater, and can be placed with directional drilling equipment independent of groundwater well casings. The soil-modifying reagent includes a variety of gases, liquids, colloids, and adsorbents that may be reactive or non-reactive with soil components. In accordance with various aspects of the invention, the method may be used to form reactive barriers, control pests, enhance soil nutrients for microbes and plants, and serve other functions.